AbstractWe have studied the ultrastructure of the testis and interstitial tissue of lizardLacerta muralissacrificed in spring, summer and autumn, with special emphasis on the morphological changes of Leydig cells. From the autumn to the end of spring, Leydig cells showed a large smooth endoplasmic reticulum and mitochondria with tubular cristae. These features correlate with the synthesis and secretion of androgens. At the end of spring and after mating, the amount of smooth endoplasmic reticulum decreased and the mitochondria showed laminar cristae. Both features are typical of a latent period, during which time secretion of androgens remains inactive until the end of summer. The possible role of other cell organelles, such as Golgi complex and lysosome‐like electron dense bodies, during both secreting and resting periods, is also discussed. Finally, we consider the relationship between seasons, secretory activity of Leydig cells and the spermatogenic cycl